Pressure transducer



NOV. 3, 1959 1 HOFFMAN 2,911,606

PRESSURE TRANSDUCER Filed July 5, 1957 K 6E 64 80 5a l 60 lNVENTOR ESL/E J.' HUFFM//V United States 1 2,911,606Y PRESSURE TRANSDUCER Leslie J.-Holman, Orange, Conn., assignor, by mesne assignments, to United Aircraft Corporation, East-Hartford, Conn., al corporation of Delaware Application July 5, 1957, SerialV No. 670,254'

16 Claims. (Cl. 338-42) Inust be biased lstrongly to accommodate the limited range of movement of the pressure sensitive element. Then too, the devices of the prior art exhibit hysteresis. The limited range of motion, furthermore, usually requires the use of an intermediate linkage or elements, suclr as gears or the like, to magnify the motion. This produces a device which has poor vibration resistance, excess weight, undue friction, nonlinearl functioning and backlash.

One vobject of my invention is to provideV an improved pressure transducer of the potentiometer type in which the pressure element is adapted to move the potentiometer brush directly without the use of intermediate elements to magnify motion.

Another object of my invention is to provide a pressure Itransducer of a simpliiied design which is light in weight and small in size.

Another objectof my invention is to provide a pressure ytransducer of the potentiometer type which has excellent resistance to shock and vibration owing to the elimination of gears, levers and beam arrangements.

Another object of my invention is to provide a pressure transducer which will function linearly and without undue friction.

Other and further objects of my invention will appear from the following description.

In the accompanying drawings, which form part of the instant specification and which are to be read inconjunction therewith and in which like reference numerals are used to indicate like parts inA the various views:

vFigure 1 is a sectional elevation of a pressure transducer showing one embodiment of my invention, with a stem broken away and the spring distended better to show its construction.

Figure 2 is a sectional view taken along the line 2-2 of Figure `1.

In general,V my invention contemplates the use of aV diaphragm comprising a fabric impregnated with a synthetic resin as a partition separating two regions, the

K pressure between which it is` desired to sense.

The textile diaphragm is pliable but not resilient and movement between them can be measured as a potential difference.v The diaphragm is biased-by a spirally cut range spring which is designed to have a long throw to accommodate the long range of travel of the textile pressure element. The design of the spring is such that no two points on it will have the same resonant frequency. This makes the spring stable in spite of vibration. The spiral spring also has lateral stability which serves as a frictionless guide for the upper end of the guidestem, as will be more fully pointed out hereinafter.

More particularly referring'now to the drawings, a body 1G is provided with an internal bore 12. An annular shoulder i4 provides a seat adapted to coact with the rim 16 of a lower closure member 18. The lower end of bore 12 is provided with internal threads 20 and is adapted to receive the externally threaded lowerclosure member 1d. Between the rim 16 of the lower closure member and the shoulder hi of the body member I clamp the peripheral edge 22 of a textile diaphragm 24'. This diaphragm may be formed of a fabric woven of nylon, (fibers of polyamide resins), Dacron (a synthetic fiber made from the condensation products of dimethyl terephthalate and ethylene glycol), glass fibers', cotton fibers or polyester fibers. The Iparticular liber of which the fabric is to be woven is determined from the use for which the pressure transducer is to be employed. The considerations of employment also govern the impregnating material, as will be pointed out more fully hereinafter.

In the case of glass iibers the average fiber diameter should not exceed l() microns. If fibers inexcess of this are employed too much resiliency is imparted to the fabric which will interfere with its use.

The weight of the fabric before impregnation is likewise determined from the pressures to be employed in my transducer. A heavier fabric, of course, will be used for higher pressure.differentials.` In general, a fabric weighing between .5 oz. per yard or less and 3 ozs. per yard or more is satisfactory for employment in my pressure transducer. 1

The fabric is impregnated with a material adapted to render it impervious to the fluid, either gas or liquid, the pressure of which is to be measured. The impregnating material must be pliable as well as impervious so that no spring rate will be introduced lby the diaphragm itself and the diaphragm may roll along the inner wall of the bore of the body during the movement of the diaphragm in response to changes of pressure.

Elastomers are ideal vsubstances for impregnation. Such elastomers as ThiokoL a synthetic rubber made by condensing ethylene dichloride and sodium tetrasulfide or dichloroethyl ether and sodium tetrasulfide, or

mixtures of these condensation products,` `neoprene l (monovinyl acetylene copolymer), ,Koroseal? (polyvinyl chloride resin), Kel-F Elastomer (trifluorochloroethylene copolymer), Teflon elastomer (tetraiiuoroethylene copolymer), Chemigum (butadiene-acrylonitrile synthetic rubber), silicone rubber (polysiloxane or polyorganosiloxane), and the like may be used as the impregnating material. Silicone rubbers, for example, are remarkable in maintaining their rubbery properties over an unusually wide range of temperatures from approximately F. to 500 F. The impregnated textile disk which forms the diaphragm 24 will have no spring rate and hence need not be considered in the system forces of the unit. Owing to the fact that it has no spring rate, the diaphragm will not introduce nonlinear characteristics into the system. Unlike other pressure sensitive means, such as bellows, flexible diaphragms, Bourdon tubes, and the like,vthe elastomer impregnated textile diaphragm has the ability to traverse a distance greater than its own initial diameter in response to pressure.

. electrical contact during vibration.

A cup 26 is secured to the upper portion of the diaphragm 24 by an appropriate adhesive. A disk 28 is secured to the lower portion of the diaphragm 24 by an adhesive. In practice the diaphragm 24 is pressure clamped between the cup 26 and the disk 28 after adhesive has been applied in order to form a good union. Any appropriate adhesive, such as epoxy resins (reaction products of epichlorohydrin and bisphenols), Furane resins (furfuryl alcohol polymers) and the like may be employed. Many of the impregnating materials employed are good adhesives of themselves. With neoprene and Thiokol elastomers, the cup 26 and the disk 28 may be pressed toward each other and thus pressure clamp the diaphragm therebetween.

It will be understood by those skilled in the art that any appropriate method for clamping the elastomer impregnated diaphragm 24 between the cup 26 and the disk 28 may be employed.

It will be observed that there is a fold 3@ of elastomer impregnated fabric around the rim 32 of the cup. As the cup moves upwardly under pressure, the fold will roll along the inner surface of the bore 12 of the body 10. This rolling action of the elastomer impregnated diaphragm allows the assembly to move upwardly through a great distance. It is understood, of course, that the adhesion of the cup is only in the area of the disk 28 and not along the sides of the cup. This enables the diaphragm to roll through a long stroke. The extended stroke makes it possible to employ smaller resolution values without increasing the size of the unit. It will also be observed that my improved assembly eliminates overstressing. The diaphragm may move through many, many cycles without crystallization, hysteresis, and the like.

Secured to the upper portion of the cup 26 in any appropriate manner, such as by adhesive or the like, l provide an insulating body member 34 upon which a resistance wire 36 is wound. The resistance wire forms the resistor of the potentiometer. The lower end of the resistor 36 is connected by a conductor 38 to one terminal 40 of a potential source, such as a battery, or the like. The upper portion of the resistor 36 is connected by a conductor 42 to the other terminal 44 of a battery, or the like. One of the terminals 444 or 40 may be grounded. One or more potentiometer brushes 46 and 48 are secured to the body member by means of screws 50. The brushes are connected by conductor 52 to ground 54. It is understood, of course, that the brushes may be insulated, if desired, in which case the ground 54 will be connected to one of the battery terminals 44 or It will be' observed that two brushes or wiper fingers are employed, one on one side of the potentiometer and one on the other. This brush construction maintains The winding 36 may belinearly wound to give a linear variation of resistance as a function of displacement of the cup 26. It is understood, of course, that the winding of the potentiometer may be nonlinear, if desired, in order to give a nonlinear function, as will be understood by those skilled in the art.

A stem 60 is secured to the upper end of the body member 34 and carries member 62. In the drawing, for ease in showing the construction, I have broken away the stem 60 and extended the spring 80. it will be understood, of course, that normally the stern 60 is a unitary member. The member 62 is provided with a flange 64 and a threaded stem 66 provided with a slot 68. The end 70 of a range spring 8l) rests upon the flange 64. A lock nut 72 is threadedly secured upon the stem 66. The range spring 80 is spirally cut of varying width. It will be observed by reference to Figure 2 that the upper region of the range spring is of narrow width, while the lower region of the range spring is wide, there being a progressive increase of width from one end of the range spring to the other. In this manner, no two points on the range spring will have the same resonant frequency. This makes the spring as a whole vibration stable. The spiral configuration of the spring` produces a long deflection characteristic which is necessary to accommodate the long travel of my elastomer impregnated textile dia phragm. The arrangement, furthermore, is such that the spring has lateral stability. This provides a frictionless guide for the upper end of the stem 60. The lower end of the range spring is positioned about a screw 82 secured to the body member 10. A washer 84 rests under the screw upon a plate 86 provided with a slot 88. By loosening the screw 82, the plate 66 may be moved backwards and forwards to increase or decrease the stiffi ness of the spring by increasing or decreasing its effective length. Another adjustment is located at the center of spring 80. This is called a Zero adjustment which properly locates the wiper fingers 46 and 48 on the resistor 36 at zero pressure. This adjustment is accomplished by member 66. After loosening locknut 72the member 66 may be moved up or down upon the stem 62 by inserting a screw driver in the slot 68 and rotating Vit. As the member 62 is turned clockwise the internal thread 62 on member 66 draws stem 60 upwards. This action positions the wiper lingers further from the end of the pot. When the member 62 is turned counterclockwise the reverse action takes place.

A cover 90 is threaded to the upper rim of the body member 10. Ordinarily, the pressure above the diaphragm 24 may be atmospheric pressure. It is to be understood, of course, that, if desired, the cover may be sealed and superatmosphericpressure be imposed above the diaphragm. If this is desired, the plug 92 is removed from the cover and pressure applied through a suitable iitting seated in the boring in which plug`92 is lodged.

It is also to be observed that a plurality of range springs may be stacked one upon the other to provide different pressure ranges.

In order to reduce friction, only one guide stem 94 is provided. The upper end of this guide stem is threadedly secured to the disk 28. The lower end is provided with a piston 96 which is positioned in a bore 98 formed in the lower member 18. The outside diameter of the piston 96 may be formed along the surface of a sphere to provide a spherical bearing. The lower end of the bore 98 below the piston 96 communicates with an opening 100 through a small duct 99 and an apertured plug 97. In this manner the piston and the bore 98 form a damping assembly of a dashpot type. The damping may be readilyY varied by replacing the plug 97 with a plug having a different aperture. It will be observed that the smaller the aperture, the higher the damping will be. The opening -100 is internally threaded and adapted to provide communication with a source of pressure which is to be measured. AThis pressure is adapted to communicate to the underside of the elastomer impregnated diaphragm 24 through a duct 95.

In use, the terminals 44 and 40 are connectedv across a source of potential. Any appropriate voltage measuring device is connected between ground 54 and one of the terminals 40 or 44, depending on their respective polarities and whether or not the throw of the Voltage measuring device is to be from a high positivevoltage to a low positive voltage, or vice versa. The range spring, of course, has been calibrated and adjusted and properly zeroed. The pressure to be measured with respect to atmospheric pressure communicates with the underside of the` textile elastomer impregnated diaphragm 24 through the duct 95. If the pressure is to be measured against atmospheric pressure, the plug 92 may be of a porous material or a strainer which permits the ready access of atmospheric pressure to the upper surface of the diaphragm 24. As pressure changes, the diaphragm will move in response to the difference in pressure. It will be observed that there is a wide throw possible for the diaphragm. The cup 32 is adapted to telescope around the boss 49 formed on the body portion 1li de' pending into the bore 12. The dashpot assembly provides adequate damping and minimizes hunting owing to pressure changes. The stem 60, being connected to the range spring, forms an upper frictionless bearing. The elastomer impregnated diaphragm. has no spring rate andthe friction of the system is a minimum, owing to the small contact area of the dashpot piston 96. The progressively decreasing width of the range spring from its bottom to its top ensures that no two portions of the spring have the same resonant frequency. This makes the spring as a whole vibration stable. The configuration of the spring provides a wide throw in a substantially linear rfashion corresponding to the throw of the elastomer impregnated diaphragm.

It will be seen that I have accomplished the objects of my invention. I have provided animproved pressure transducer of the potentiometer type in which the pressure element is adapted to move relative to the potentiometer brush directly and without the use of intermediate elements commonly employed in the devices of the prior art to magnify motion. The elimination oif the intermediate elements simplies the design and increases the resistance of the assembly to shock and vibration. An accurate reading may be maintained with my pressure transducer owing to the large relative movement of the potentiometer brush for a given increment of pressure change. v

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and 'subcombinations This is contemplated by and is within the scope ofmy claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. it is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. A pressure transducer including in combination a housing having an inner wall surface, a movable member positioned in said housing, said member providing a surface spaced from said inner surface, an impervious flexible diaphragm secured to said member and to said housing to divide said housing into two spaces, said diaphragm having a portion disposedin the space between said member surface and said housing wall surface, means providing communication between a source of uid pressure to vbe measured and one of said spaces, means biasing said member to a position adjacent one end of said housing against the action of said fluid pressure, said diaphragm portion having a dimension which permits the portion to be forced against said member surface under the action of uid pressure when said member is in said position to which it is biased, said diaphragm portion rolling away from said member surface when the member moves from said position adjacent one end of the housing toward the other end of the housing and means responsive to movement of the member for producing an electrical potential which afords a measure of the uid pressure being measured.

2. A pressure transducer including in combination a housing having an inner cylindrical wall surface, a movable member formed with a cylindrical surface, means positioning said member in said housing with its cylindrical surface substantially parallel to and spaced from said cylindrical wall surface, an impervious exible diaphragm secured to said member and to said housing to divide said housing into two spaces, said diaphragm having a portion disposed in the space between said cylindrical surfaces, means providing communication between a source of fluid pressure to be measured and one of said spaces, means biasing said member to a position adjacent one end of said housing against the action of said uid pressure, said diaphragm portion having a dimension which permits said portion to be forced against the member cylindrical surface under the action of fluid pressure when said member is in said position to which it is biased, said diaphragm portion rolling away from said member cylindrical surface when said member moves from its position adjacent said one end of the housing toward the other end of the housing under the action of fluid pressure acting against said biasing means and means responl sive to movement of the member for producing a potential affording a measure of said fluid pressure.

3 A pressure transducer as in claim 2 in which said fabric is a textile woven from nylon fibers.

4. A pressure transducer as in claim 2 in which said fabric is a textile woven from Dacron fibers.

5. A pressure transducer as in claim 2 in which said fabric is a textile woven for polyester fibers.

6. A pressure transducer as in claim 2 in which said eiastomer is a silicone rubber.

7. A pressure transducer as in -claim 2 in which said elastomer is Teiion elastomer.

8. A pressure transducer as in claim 2 in which said elastomer is Kel-F Elastomer.

9. A pressure transducer as in claim 2 in which said elastomer is ThiokoL l0. A pressure transducer as in claim 2 in which said elastomer is neoprene.

11. A pressure transducer as in claim 2 in which said biasing means comprises a spiral spring.

12. A pressure transducer as in claim 2 in which said biasing means comprises a spiral spring formed with progressively varying width.

13. A pressure transducer as in claim 2 in which said biasing means is a spiral spring, and means 'for varying he spring rate. i

14.v A pressure transducer including in combination a hou`sing,ra textile diaphragm separating the housing into two spaces, an elastomer impregnating said diaphragm and rendering it impervious to the passage of fluids, a potentiometer having a brush and a winding mounted respectively on said housing and said diaphragm, a spiral spring for biasing said diaphragm, means for damping said diaphragm and means for providing communication between a source of fluid pressure to be measured and one of said spaces.

15'. A pressure transducer as in claim 14 in which said damping means comprises a dashpot having a cylinder and a piston and means for attaching said piston rto said diaphragm.

16. A pressure transducer as in claim 14 in which said damping means comprises a dashpot having a cylinder and a piston, means for attaching said piston to said diaphragm and means providing communication between the cylinder below said piston and the uid pressure to be measured. Y

References Cited in the le of this patent UNrTnD STATES PATENTS 140,084 Slicer June 17, 1873 488,121 Houghton et al Dec. 13, 1892 1,036,233 Heeley Aug. 20, 1912 1,694,286 Shorts Dec. 4, 1928 2,474,662 Fuller June 28, 1949 2,515,867 Fuller July 18, 1950 KA2,620,665 Carlisle et al Dec. 9, 1952 2,698,816 Dosmann et al Jan. 4, 1955, 2,710,266 Hochberg lune 7, 1955' 2,742,785 St. Clair Apr. 24, 1956 2,750,305 Gagarine et al June 12, 1956 FOREIGN PATENTS 669,669 France Nov. 19, 1929 717,124 Germany Feb. 6, 1942 686,314 Great Britain Jan. 21, 1953 502,636 Canada May 18, 1954 

